DE69311739T2 - PRODUCTION OF A DETERGENT - Google Patents

Description

The invention relates to the preparation of compounds of the general formula:

ROSO3H,

wherein R represents a primary alkyl group. The compounds are primary alkyl half esters of sulfuric acid. They are the acid form of primary alkyl sulfate, variously known as primary alcohol sulfate, which is an anionic detergent.

Primary alkyl sulfate (PAS) of the formula:

ROSQ&sub3;M,

where R is a straight or branched alkyl chain having 8 to 20 carbon atoms and

M stands for a solubilizing cation, such as sodium or ammonium, has been known for many years as an anionic detergent.

Primary alkyl sulfate is usually prepared by sulfonating the corresponding primary alcohol to produce the acid form of the detergent (PAS acid).

This form of acid is then neutralized to produce the detergent itself, so the production process is:

ROH T ROSO&sub3;H T ROSO&sub3;N.

Sulfonation of the primary alcohol can be carried out using sulfur trioxide in a conventional sulfonation/sulfonation reaction facility.

However, a known problem is that the resulting PAS acid is unstable and spontaneously reverts to the primary alcohol. If the PAS acid is stored at ambient temperature, a significant portion of the starting alcohol decomposes within 24 hours. Moderate cooling below ambient temperature reduces the degree of decomposition but does not solve this problem. Consequently, it is necessary to use the PAS acid immediately after it has passed through the This reduces the flexibility in managing the entire manufacturing process and is also impractical because the physical properties of PAS acid would allow for easier handling and transportation than the paste produced by neutralization.

When spontaneous decomposition of PAS acid occurs, it results in the formation of the original primary alcohol which was the starting material for sulfonation and also sulfuric acid. When the mixture is neutralized and analyzed, the desired primary alkyl sulfate is found to contain an inorganic salt such as sodium sulfate which is formed by the neutralization of sulfuric acid which is the product of the decomposition and also primary alcohol which is formed by the decomposition. The usual analysis usually provides a percentage of so-called non-detergent organic matter (NDOM), often referred to as "free oil" (FO), which includes the decomposition product of primary alcohol and also primary alcohol from the starting material which was not reacted during sulfonation.

As explained below, the invention makes use of compounds containing alkylene oxide residues, the presence of which leads to the introduction of trace amounts of dioxane compounds, the presence of which in the product is undesirable.

The present invention primarily aims to inhibit the spontaneous decomposition of PAS acid. Preferred embodiments of the invention are directed to this, while also keeping the dioxane impurities at low levels.

In the broadest sense, we have now found that the spontaneous decomposition of PAS acid can be effectively inhibited by the presence of alkylene oxide residues, which may also be called alkyleneoxy groups, and by hydroxyalkyleneoxy groups.

In the broadest sense, the first aspect of the invention provides a process for preparing and stabilizing a primary alkyl sulfuric acid of the formula:

ROSO3H,

wherein R represents a straight or branched saturated primary alkyl group having 8 to 22 carbon atoms, the process comprising: sulfonating a raw material comprising the corresponding primary alcohol of the formula:

RAW

by producing a sulphated reaction product and adding to the raw material and/or the reaction product before, during and/or after sulphating a compound or a mixture of compounds which include alkyleneoxy radicals or hydroxyalkyleneoxy groups as a stabiliser, wherein the proportion of the alcohol ROH in the raw material exceeds the proportion of the compounds which include alkyleneoxy radicals or hydroxyalkyleneoxy groups, if at all.

The invention results in a mixture containing the primary alkyl sulfuric acid and the stabilizer. Such a mixture forms a further aspect of the invention.

The amount of stabilizer is usually less than the amount of primary alkyl sulfuric acid. In particular, the weight ratio of primary alkyl sulfuric acid to stabilizer may be in the range 20:1 to 2:1.

The group R can advantageously be a saturated alkyl group having 8 to 15 carbon atoms.

Usually the primary alkyl group R is a mixture of saturated, straight or branched alkyl chains having on average 11 to 18 carbon atoms, with the range 12 to 15 carbon atoms being particularly preferred.

The stabilizer can be a wide variety of compounds represented by the general formula:

Y(A) nX,

wherein A represents an alkylene oxide radical or a hydroxyalkyleneoxy group, n represents a positive number and Y and X can be a substantial number of end groups. Without being bound to any theory regarding the mode of action of the stabilizer, it is believed that the stabilization by the oxygen atoms representing ether bonds and those by the alkylene oxide radicals or hydroxyalkyleneoxy groups These ether oxygen atoms are likely to temporarily bind hydrogen ions and prevent those ions from participating in the decomposition process of the primary alkyl sulfate. This does not, of course, exclude the possibility of other stabilizing effects acting simultaneously or alternatively, particularly in the case where Y and X are hydrogen, so that the stabilizer has a hydroxyl group which can advantageously participate in an alternative stabilizing mechanism.

It is preferred that the stabilizer includes residues of an alkylene oxide having 2 to 4 carbon atoms, especially ethylene oxide.

An alkylene oxide residue can also be an alkylene oxide group of the formula:

- (OW) -

where W is a divalent alkylene group. A hydroxyalkyleneoxy group has the formula:

in which - represents a hydroxy-substituted alkylene group, in particular hydroxypropyl or hydroxyisopropyl.

It is also preferred that the stabilizer should have surfactant properties. It can then serve as an additional detergent in a detergent product which incorporates the primary alkyl sulfate obtained by ultimate neutralization of the acid form.

Preferred stabilizers are therefore compounds and mixtures of compounds that satisfy the general formula:

R¹(A)nX,

wherein R¹ represents a straight or branched primary alkyl group having 8 to 22 carbon atoms, A as above and X is hydrogen, -OSO₃H or an alkyl group having 1 to 8, preferably 1 to 4, carbon atoms. When X is an alkyl group, for example, methyldioxane formation can advantageously be suppressed. The average value of n may be in the range 0.5 to 4 or possibly higher, for example 0.5 to 10 or more. More preferably, the value of n is at least 1. It may be preferred that the value of n is not more than 3. A range of 1.5 to 2.5 is particularly possible. R¹ may advantageously be saturated alkyl having an average chain length of not more than 18 carbon atoms and may have on average at least 11 carbon atoms and preferably 11 to 15 carbon atoms.

As already mentioned, the amount of stabilizer is usually less than the amount of PAS acid. The weight ratio of acid to stabilizer is preferably in the range of 20:1 to 1.5:1. The amount of stabilizer may be sufficient so that the range does not exceed 10:1 or even 9:1. At the other end of the range, the amount of stabilizer may be such that the range does not exceed 3:1 or even 4:1.

Preferably, the ratio of the number of PAS acid molecules to alkylene oxide residues or hydroxyalkyleneoxy groups of the stabilizer is greater than 1:1, i.e. PAS acid molecules are numerically superior to the alkylene oxide residues and hydroxyalkyleneoxy groups.

Sulphation is preferably carried out using sulfur trioxide.

The invention is not limited to any particular apparatus for carrying out the chemical reaction that forms PAS acid. A common embodiment is sulfonation using sulfur trioxide in a reactor that provides a high surface area for contact between the reactants. A falling-film reactor is typically used.

After the sulfonation has been carried out, the stabilizer can be added to the PAS acid. Alternatively or additionally, the stabilizer or a precursor thereof can be added to the primary alcohol can be added before carrying out the sulphation or even during the course of the sulphation if the equipment allows it.

To reduce dioxane contamination, it is preferred to add the stabilizer after sulfonation has taken place, even if some was added before or during sulfonation. The addition preferably takes place immediately after the PAS acid leaves the reactor in which sulfonation took place. Preferably this takes place after no more than 15 minutes, more preferably after no more than 5 minutes.

Preferred stabilizers for addition after sulfonation are compounds and mixtures of compounds of the formula:

R¹(A)nOX,

wherein A represents an alkylene oxide radical having 2 to 4 carbon atoms and X represents a hydrogen atom or an alkyl group having 1 to 8, preferably 1 to 4, carbon atoms, while R¹ and n are as defined above.

If the stabilizer of formula R¹(A)nOX is a substance where X is hydrogen, some of it can be sulfonated very quickly by residual sulfur trioxide contained in the PAS acid. The resulting product of formula:

R¹(A)nOSO₃H

is the acid form of alkyl ether sulfate, which can also serve as an anionic detergent after neutralization, especially when A represents an ethylene oxide residue.

Stabilizers of the formula R¹(A)nOX, where X is hydrogen, are non-ionic surfactants. Stabilizers of this type, which do not react before neutralization, therefore provide a proportion of non-ionic surfactant in the neutralized mixture and in the products made therefrom.

When the stabilizer or a precursor thereof is incorporated into the primary alcohol prior to sulfonation, preferably a compound of the formula:

R¹(A)nOH

where R¹, n and A are as defined above. This compound is then sulfonated at the same time as the primary alcohol so that the sulfonated mixture contains as a stabilizer a compound of the formula:

R¹ (A) nOSO₃H

contains. The use in the primary alcohol before sulfonation can be carried out by treating the alcohol with alkylene oxide, so that the raw material containing an alcohol is converted into a mixture of alcohol and alkoxylated alcohol.

This mixture corresponds to the general formula:

R(A)pOH,

where p has a mean value; which is preferably in the range 0.1 to 0.5.

When alcohol ethoxylate of the formula R¹(A)nOH is prepared separately and added before sulfonation, or when an alkyl ether sulfuric acid of the formula R¹(A)nOSO₃H is added after or before sulfonation, it is desirable that the final mixture of alkyl sulfuric acid and alkyl ether sulfuric acid conforms to the general formula:

R¹(A)pOSO₃H,

where p has a mean value of 0.1 to 0.5.

When the stabilizer or a precursor thereof is present in the raw material prior to sulfonation, either by addition to the primary alcohol or by treating primary alcohol with alkylene oxide, the amount of alkoxylated compound ultimately included in the raw material is limited by the requirement that the proportion of alcohol in the raw material should exceed the proportion of compounds containing alkylene oxide or hydroxyalkyleneoxy groups.

It may be noted that the usual preparation of alkyl ether sulfate involves the sulfation of an alkoxylated alcohol which includes a proportion (which may be quite small) of alcohol itself. In such a preparation the alcohol sulfuric acid formed was only a minor component of little importance.

If the raw material contains only a small proportion (or none at all) of material other than the alcohol and compounds containing alkylene oxide or hydroxyalkyleneoxy groups, then the reaction product contains a predominant amount of primary alkyl sulfuric acid by weight. This is an essential embodiment of the invention.

Although the present invention requires that the raw material contain the alcohol in a greater amount than the compounds (if any) containing alkylene oxide residues or hydroxyalkyleneoxy groups, it is possible that other materials may be present in the raw material. Moreover, these may undergo reactions.

In particular, the raw material may contain another substance that undergoes sulphonation or sulfonation simultaneously with the sulphonation of the primary alcohol. In particular, the raw material could contain alkylbenzene that undergoes sulphonation to alkylbenzenesulphonate. The reaction product would then be a mixture of the acid forms of primary alkyl sulphate and alkylbenzenesulphonate.

The final mixture of PAS acid and stabilizer provided by this invention can be stored for several hours, at least prior to neutralization. The shelf life of the PAS acid before significant decomposition has occurred is significantly extended by the addition of stabilizer according to the invention if storage takes place in any temperature range, for example 0°C to 40°C. However, if storage takes place at a temperature towards the lower end of this range, preferably 0°C to 20°C, more preferably 0°C to 10°C, especially 0°C to 5°C, the rate of decomposition of the reaction mixture reduced by the lower temperature and by the stabilizing effect. Consequently, the storage time in the presence of stabilizer can be increased relative to the possible storage time at higher temperature in the presence of the same stabilizer. Use at lower temperatures is also valuable for inhibiting the formation of dioxane, which, as already mentioned, is an undesirable contaminant.

The use of the stabilizer in the PAS acid at a temperature at which the PAS acid is liquid is preferred.

In the examples below, all quantities and percentages are based on weight, unless otherwise stated.

example 1

This example starts with a fatty alcohol of the formula:

RAW,

where R is a mixture of straight and branched alkyl groups (about 60% branched), mainly with 12 and 13 carbon atoms. This alcohol, prepared by the OXO process, was commercially available as LIAL 123.

The alcohol was sulphated using sulphur trioxide and a pilot plant with a falling film reactor. Three batches of the resulting PAS acid were taken from the subsequent trickle film reactor. One batch was left at 30ºC for 24 hours. A second batch was left at 10ºC for the same period. A third batch was immediately mixed with non-ionic surfactant as a stabiliser in an amount constituting 15% of the resulting mixture (i.e. an 85:15 weight ratio of reaction product:stabiliser). It was then also stored at 10ºC. This non-ionic surfactant was coconut alcohol (mainly 012 and 014) ethoxylated under reaction conditions which yield a high proportion of molecules with up to four ethylene oxide residues and a very low proportion with six or more ethylene oxide residues. This was a so-called "Peaked Nonionic" (nonionic surfactant with a narrow molecular weight range) according to the general formula:

R¹(A)nOH,

where R¹ represents mainly linear C₁₂ and C₁₄ alkyl ,

A represents an ethylene oxide residue and

n has a mean value of 2.0.

Portions of each batch of PAS acid were periodically removed, neutralized with sodium hydroxide solution and analyzed for the content of sulfate detergent (SD) and sulfate-free organic matter (SFOM).

The neutralization conditions were calculated in such a way that an aqueous lye with a theoretical proportion of anionic detergent of about 25 wt.% is produced.

The analytical results for sulfate-free organic matter are expressed as a percentage of the amount of anionic detergent found in the analysis.

Portions of the third batch were also analyzed for dioxane content. The amount of this contaminant was expressed as parts per million (ppm) based on the amount of anionic surfactant found in the analysis.

The following results were obtained:

It is evident from these results, particularly from the flush values for sulfate-free organic matter, that without stabilizer the spontaneous decomposition is considerable at 30ºC and is still significant at 10ºC.

With stabilizer added, decomposition is less. The number for the anionic sulfate detergent (SD) starts low due to the addition of stabilizer. It then drops to a lesser extent than it does without stabilizer. The number for sulfate-free organic matter is higher because stabilizer appears in it. The number drops initially due to small amounts of unreacted alcohol and sulfur trioxide in the PAS-acid reaction product. If the reaction product is stirred prior to neutralization, some of the sulfur trioxide can react with the stabilizer and this causes the slight drop in the SFOM value. Thereafter, the SFOM value remains almost constant.

An "ideal" value for SFOM was calculated based on two assumptions:

1) Sulfation would yield a mixture containing small amounts of unreacted sulfur trioxide and alcohol (as normally observed) such that if neutralized prior to decomposition, the PAS acid would result in a PAS:alcohol:Na₂SO₄ ratio of 100:1.5:1.5.

2) Unreacted sulfur trioxide would be combined with some stabilizer, converting it into detergent.

The value predicted for SFOM in this way was 14.6%, close to the observed values.

Example 2

In this example, commercially available fatty alcohol (LIAL 125) of the formula:

RAW

where R represents a mixture of straight and branched alkyl groups, mainly with 12 to 15 carbon atoms.

Sulphate as in Example 1. Three batches were collected and stored at 0º to 5ºC.

To one batch no stabilizer was added. A second of these batches was immediately mixed with a stabilizer, namely the same as used in Example 1. This was pre-cooled to a temperature below 5°C before addition. It was added as in Example 1 in an amount providing 15% by weight of the resulting mixture.

The third batch was also immediately mixed with a stabilizer in an amount providing 15% by weight of the resulting mixture. This stabilizer was again a peaked nonionic surfactant obtained by ethoxylation of LIAL 125. It satisfied the general formula:

R(A)nOH,

where R is as in LIAL 125, A is an ethylene oxide residue and n has an average value of 2.0.

Portions were taken from each batch at intervals and neutralized with sodium hydroxide under conditions calculated to give an aqueous liquor containing a theoretical anionic detergent content of about 20% by weight.

The resulting neutralized samples were analyzed and the results are given below for the sulfated detergent (SD) level. For the batches that received stabilizers, the results are also given for sulfate free organic matter (SFOM) and dioxane level. As in the previous example, these results are given as percentages and parts per million of the amount of anionic detergent found in the analysis.

(ND means dioxane was below the detection limit of 15 ppm, based on the amount of anionic surfactant).

As can be seen from these results, by adding stabilizer at low temperature, the decomposition is reduced and the formation of dioxane is low.

Example 3

This example also uses a fatty alcohol LIAL 125. It was ethoxylated according to the general formula:

R(OCH2CH2)pOH,

where p has a mean of 0.25.

It was then sulphonated as in Example 1. Four batches were collected. One was kept at 20ºC, another at 0ºC to 3ºC. Two more were mixed with another stabiliser in an amount that was 15% of the total mixture. This additional stabiliser was LIAL 125, ethoxylated to contain an average of two ethylene oxide residues as used in Example 2 and was kept at 20ºC and 0ºC to 3ºC respectively.

Pieces from each batch were taken, neutralized and analyzed as in the previous example. The results obtained are outlined in the table below.

The "ideal" value for SFOM, calculated as in Example 1, was 14.5% in the presence of stabilizer.

The results in the first two columns are for a system where the stabilizer was the alkyl sulfuric acid product of the ethoxylated alcohol present in the starting alcohol. These results show an improvement over the results without any stabilizer in the previous examples, demonstrating the benefit of using alkyl ether sulfuric acid. The addition of nonionic surfactant as a stabilizer after sulfonation provided a further significant improvement.

Example 4

LIAL 123 was sulfonated to produce PAS acid as in Example 1. Stabilizers were then added to a batch of PAS acid to provide an 85:15 weight ratio of reaction product to stabilizers and stored at a constant temperature as listed below.

A : LIAL 123 with an average degree of ethoxylation of 3

B : LIAL 125 with an average degree of ethoxylation of 2

C : LIAL 125 with an average degree of ethoxylation of 3

D : Coconut oil with an average degree of ethoxylation of 3

B, C and D were ethoxylates with a narrow molecular weight range.

Samples were then periodically taken from each batch and neutralized as in Example 2 and analyzed to determine the amount of non-detergent organic matter (NDOM) and the amount of dioxane contained therein. The results are presented in the tables below and the NDOM figures in wt.% and ppm, based on the amount of anionic detergent detected.

The above NDOM numbers do not vary significantly with time, indicating that PAS acid has not degraded to any significant extent. In addition, the results show that dioxane formation is suppressed by storing the batch at lower temperatures and by using a narrow molecular weight range ethoxylate as a stabilizer.

Example 3

LIAL 125 alcohol was sulphated to provide PAS acid with at least 97% purity, 2 batches of PAS acid were collected and mixed together with a stabiliser in a weight ratio of 85:15 and stored at a temperature of 0 to 5ºC. The stabilisers used were LIAL 125 with an average degree of ethoxylation of 2 (narrow molecular weight range (batch 5.1)) and non-ionic surfactant with methyl end groups and an average degree of ethoxylation of 6.5 and available under the trade name REWOPAL MT65 from REWO (batch 5.2).

Samples were taken from each batch after 1 hour and 24 hours and neutralized as in Example 2 and analyzed to determine NDOM and dioxane levels.

The results are presented below.

The results show that the PAS acid does not degrade significantly and dioxane levels are maintained at a low level over time. In addition, the stabilizer in batch 5.2 has a higher degree of ethoxylation than that of batch 5.1. Thus, a higher amount of dioxanes would be expected to be obtained. However, the results show only a negligible difference in dioxane formation, illustrating the beneficial effect of using stabilizers protected with M groups.

Claims (10)

1. Process for the preparation and stabilization of a primary alkyl sulfuric acid of the formula: ROSO3H, wherein R represents a straight or branched saturated primary alkyl group having 8 to 22 carbon atoms, the process comprising: sulfonating a raw material comprising the corresponding primary alcohol of the formula: RAW by producing a sulphonated reaction product and adding to the raw material and/or the reaction product before, during and/or after sulphonation a compound or a mixture of compounds which include alkyleneoxy radicals or hydroxyalkyleneoxy groups as a stabiliser, wherein the proportion of the alcohol ROH in the raw material exceeds the proportion of the compounds which include alkyleneoxy radicals or hydroxyalkyleneoxy groups, if at all. 2. The process of claim 1, wherein the weight ratio of primary alkyl sulfuric acid and stabilizer is in the range 20:1 to 2:1. 3. A process according to claim 1 or claim 2, wherein the group R is a straight or branched saturated primary alkyl group having 8 to 15 carbon atoms. 4. Process according to one of the preceding claims, wherein the stabilizer contains alkyleneoxy radicals of the formula: -OCH₂(CH₂)m- , where m is an integer from 1 to 3. 5. A process according to any one of the preceding claims, wherein the stabilizer is added to the reaction product after the sulfonation. 6. A process according to claim 1, claim 2 or claim 3, wherein one or a mixture of compound(s) including alkyleneoxy radicals or glycidyl groups is/are included in the primary alcohol so as to provide a stabilizer in the reaction product after sulfonation. 7. The process of claim 6, wherein the primary alcohol is treated with an alkylene oxide prior to sulfonation, so that it forms a mixture of compounds of the formula: R(A)pOH wherein A is an alkyleneoxy radical of the formula -OCH₂(CH₂)m-, wherein m is 1 to 3 and p has an average value of not more than 0.5. 8. A process according to any one of the preceding claims, wherein the stabilizer is a compound or a mixture of compounds of the formula: R¹(A)nOX, wherein R¹ represents a straight or branched primary alkyl group having 8 to 22 carbon atoms, A represents a lower alkyleneoxy radical having 2 to 4 carbon atoms, n is in the range 0.5 to 4 and X is hydrogen, -OSO₃H or an alkyl group having 1 to 8 carbon atoms. 9. The process according to claim 8, wherein X is hydrogen or a lower alkyl group having 1 to 4 carbon atoms. 10. Agent comprising 50 to 95% primary alkyl sulphuric acid of the formula: ROSO&sub3;H where R is a straight or branched primary alkyl group having 8 to 22 carbon atoms and 5 to 50% of a stabilizer, namely a compound or mixture of compounds including alkyleneoxy radicals or glycidyl groups. -11. Agent according to claim 10, wherein the stabilizer is a compound or a mixture of compounds of the formula: R¹(A)nOX where R¹ is a straight or branched primary alkyl group having 8 to 22 carbon atoms; which may be the same as or different from the group R, A represents a lower alkyleneoxy radical with 2-4 carbon atoms, X is hydrogen, -OSO₃H or a lower alkyl group having 1 to 8 carbon atoms, and n is in the range 0.5 to 4.